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• Sync Vs. Async Sockets Performance in .NET

  - by Michael Covelli

  Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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• Windows could not start the Apache2 on Local Computer - problem

  - by vaske

  During the installation of Apache2 I got the following message into cmd window: Installing the Apache2.2 service The Apache2.2 service is successfully installed. Testing httpd.conf.... Errors reported here must be corrected before the service can be started. httpd.exe: Could not reliably determine the server's fully qualified domain name , using 192.168.1.3 for ServerName (OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. : make_sock: could not bind to address 0.0.0.0:80 no listening sockets available, shutting down Unable to open logs Note the errors or messages above, and press the key to exit. 24... and after installing everything look fine, but it isn't. If I try to start service I got the following message: Windows could not start the Apache2 on Local Computer. For more information, review the System Event Log. If this is a non-Micorsoft service, contact the service vendor, and refer to service-specific error code 1. Apach2 version is 2.2.9 Does anyone have the same problem, or could help me.

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• Memory mapped files and "soft" page faults. Unavoidable?

  - by Robert Oschler

  I have two applications (processes) running under Windows XP that share data via a memory mapped file. Despite all my efforts to eliminate per iteration memory allocations, I still get about 10 soft page faults per data transfer. I've tried every flag there is in CreateFileMapping() and CreateFileView() and it still happens. I'm beginning to wonder if it's just the way memory mapped files work. If anyone there knows the O/S implementation details behind memory mapped files I would appreciate comments on the following theory: If two processes share a memory mapped file and one process writes to it while another reads it, then the O/S marks the pages written to as invalid. When the other process goes to read the memory areas that now belong to invalidated pages, this causes a soft page fault (by design) and the O/S knows to reload the invalidated page. Also, the number of soft page faults is therefore directly proportional to the size of the data write. My experiments seem to bear out the above theory. When I share data I write one contiguous block of data. In other words, the entire shared memory area is overwritten each time. If I make the block bigger the number of soft page faults goes up correspondingly. So, if my theory is true, there is nothing I can do to eliminate the soft page faults short of not using memory mapped files because that is how they work (using soft page faults to maintain page consistency). What is ironic is that I chose to use a memory mapped file instead of a TCP socket connection because I thought it would be more efficient. Note, if the soft page faults are harmless please note that. I've heard that at some point if the number is excessive, the system's performance can be marred. If soft page faults intrinsically are not significantly harmful then if anyone has any guidelines as to what number per second is "excessive" I'd like to hear that. Thanks.

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• java.net.SocketException: Software caused connection abort: recv failed; Causes and cures?

  - by IVR Avenger

  Hi, all. I've got an application running on Apache Tomcat 5.5 on a Win2k3 VM. The application serves up XML to be consumed by some telephony appliances as part of our IVR infrastructure. The application, in turn, receives its information from a handful of SOAP services. This morning, the SOAP services were timing out intermittently, causing all sorts of Exceptions. Once these stopped, I noticed that our application was still performing very slowly, in that it took it a long time to render and deliver pages. This sluggishness was noticed both on the appliances that consume the Tomcat output, and from a simple test of requesting some static documents from my web browser. Restarting Tomcat immediately resolved the issue. Cracking open the localhost log, I see a ton of these errors, right up until I restarted Tomcat: WARNING: Exception thrown whilst processing POSTed parameters java.net.SocketException: Software caused connection abort: recv failed After a big of Googling, my working theory is that the SOAP issue caused my users to get errors, which caused them to make more requests, which put an increased load on the application. This caused it to run out of available sockets to handle incoming requests. So, here's my quandary: 1. Is this a valid hypothesis, or am I just in over my head with HTTP and Tomcat? 2. If this is a valid hypothesis, is there a way to increase the size of the "socket queue", so that this doesn't happen in the future? Thanks! IVR Avenger

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• Non-blocking TCP buffer issues.

  - by Poni

  Hi! I think I'm in a problem. I have two TCP apps connected to each other which use winsock I/O completion ports to send/receive data (non-blocking sockets). Everything works just fine until there's a data transfer burst. The sender starts sending incorrect/malformed data. I allocate the buffers I'm sending on the stack, and if I understand correctly, that's a wrong to do, because these buffers should remain as I sent them until I get the "write complete" notification from IOCP. Take this for example: void some_function() { char cBuff[1024]; // filling cBuff with some data WSASend(...); // sending cBuff, non-blocking mode // filling cBuff with other data WSASend(...); // again, sending cBuff // ..... and so forth! } If I understand correctly, each of these WSASend() calls should have its own unique buffer, and that buffer can be reused only when the send completes. Correct? Now, what strategies can I implement in order to maintain a big sack of such buffers, how should I handle them, how can I avoid performance penalty, etc'? And, if I am to use buffers that means I should copy the data to be sent from the source buffer to the temporary one, thus, I'd set SO_SNDBUF on each socket to zero, so the system will not re-copy what I already copied. Are you with me? Please let me know if I wasn't clear.

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• How do I fix my "Stream closed" error in spring-ws?

  - by mcherm

  I have working code using the spring-ws library to respond to soap requests. I moved this code to a different project (I'm merging projects) and now it is failing. I would like to figure out the reason for the failure. The symptom I get is this: when the HTTP request arrives, spring begins handling the call. Then I get the following exception: org.springframework.ws.soap.saaj.SaajSoapEnvelopeException: Could not access envelope: java.io.IOException: Stream closed; nested exception is javax.xml.soap.SOAPException: java.io.IOException: Stream closed at org.springframework.ws.soap.saaj.SaajSoapMessage.getEnvelope(SaajSoapMessage.java:109) <<more lines that don't matter>> Caused by: java.io.IOException: Stream closed at java.io.PushbackInputStream.ensureOpen(PushbackInputStream.java:57) at java.io.PushbackInputStream.read(PushbackInputStream.java:116) at org.apache.xerces.impl.XMLEntityManager$RewindableInputStream.read(Unknown Source) at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(Unknown Source) at org.apache.xerces.impl.XMLVersionDetector.determineDocVersion(Unknown Source) at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source) at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source) at org.apache.xerces.parsers.XMLParser.parse(Unknown Source) at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source) at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source) at org.apache.xerces.jaxp.SAXParserImpl.parse(Unknown Source) at org.apache.axis.encoding.DeserializationContext.parse(DeserializationContext.java:227) at org.apache.axis.SOAPPart.getAsSOAPEnvelope(SOAPPart.java:696) ... 30 more Examining it in a debugger, it appears that spring successfully handles HTTP headers, but then when it begins to process the contents of the SOAP message itself, it chokes when reading the very first character of the body. Some googling for the error message suggests that the problem is that a PushbackInputStream which is apparently used for reading from the socket is read twice or perhaps has close() called and then is read afterward. It is happening inside of spring-ws, not my code, and since it worked fine before I moved the code to a new project it must have something to do with versions of spring, or something it uses like axis or xerces. But I can't find any differences in versions of these! Has anyone encountered this error before? Or do you have any suggestions of approaches I could take in troubleshooting this?

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• Automatically release resources RAII-style in Perl

  - by Philip Potter

  Say I have a resource (e.g. a filehandle or network socket) which has to be freed: open my $fh, "<", "filename" or die "Couldn't open filename: $!"; process($fh); close $fh or die "Couldn't close filename: $!"; Suppose that process might die. Then the code block exits early, and $fh doesn't get closed. I could explicitly check for errors: open my $fh, "<", "filename" or die "Couldn't open filename: $!"; eval {process($fh)}; my $saved_error = $@; close $fh or die "Couldn't close filename: $!"; die $saved_error if $saved_error; but this kind of code is notoriously difficult to get right, and only gets more complicated when you add more resources. In C++ I would use RAII to create an object which owns the resource, and whose destructor would free it. That way, I don't have to remember to free the resource, and resource cleanup happens correctly as soon as the RAII object goes out of scope - even if an exception is thrown. Unfortunately in Perl a DESTROY method is unsuitable for this purpose as there are no guarantees for when it will be called. Is there a Perlish way to ensure resources are automatically freed like this even in the presence of exceptions? Or is explicit error checking the only option?

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• image analysis and 64bit OS

  - by picciopiccio

  I developed a C# application that makes use of Congex vision library (VPro). My application is developed with Visual Studio 2008 Pro on a 32bit Windows PC with 3GB of RAM. During the startup of application I see that a large amount of memory is allocated. So far so good, but when I add many and many vision elaboration the memory allocation increases and a part of application (only Cognex OCX) stops working well. The rest of application stills to work (working threads, com on socket....) I did whatever I could to save memory, but when the memory allocated is about 700MB I begin to have the problems. A note on the documentation of Cognex library tells that /LARGEADDRESSWARE is not supported. Anyway I'm thinking to try the migration of my app on win64 but what do I have to do? Can I simply use a processor with 64bit and windows 64bit without recompiling my application that would remain a 32bit application to take advantage of 64bit ? Or I should recompile my application ? If I don't need to recompile my application, can I link it with 64bit Congnex library? If I have to recompile my application, is it possible to cross compile the application so that my develop suite is on a 32bit PC? Every help will be very appreciated!! Thank in advance

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• java BufferedReader specific length returns NUL characters

  - by Bastien

  I have a TCP socket client receiving messages (data) from a server. messages are of the type length (2 bytes) + data (length bytes), delimited by STX & ETX characters. I'm using a bufferedReader to retrieve the two first bytes, decode the length, then read again from the same bufferedReader the appropriate length and put the result in a char array. most of the time, I have no problem, but SOMETIMES (1 out of thousands of messages received), when attempting to read (length) bytes from the reader, I get only part of it, the rest of my array being filled with "NUL" characters. I imagine it's because the buffer has not yet been filled. char[] bufLen = new char[2]; _bufferedReader.read(bufLen); int len = decodeLength(bufLen); char[] _rawMsg = new char[len]; _bufferedReader.read(_rawMsg); return _rawMsg; I solved the problem in several iterative ways: first I tested the last char of my array: if it wasn't ETX I would read chars from the bufferedReader one by one until I would reach ETX, then start over my regular routine. the consequence is that I would basically DROP one message. then, in order to still retrieve that message, I would find the first occurence of the NUL char in my "truncated" message, read & store additional characters one at a time until I reached ETX, and append them to my "truncated" messages, confirming length is ok. it works also, but I'm really thinking there's something I could do better, like checking if the total number of characters I need are available in the buffer before reading it, but can't find the right way to do it... any idea / pointer ? thanks !

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• EPIPE blocks server

  - by timn

  I have written a single-threaded asynchronous server in C running on Linux: The socket is non-blocking and as for polling, I am using epoll. Benchmarks show that the server performs fine and according to Valgrind, there are no memory leaks or other problems. The only problem is that when a write() command is interrupted (because the client closed the connection), the server will encounter a SIGPIPE. I am doing the interrupted artifically by running the benchmarking utility "siege" with the parameter -b. It does lots of requests in a row which all work perfectly. Now I press CTRL-C and restart the "siege". Sometimes I am lucky and the server does not manage to send the full response because the client's fd is invalid. As expected errno is set to EPIPE. I handle this situation, execute close() on the fd and then free the memory related to the connection. Now the problem is that the server blocks and does not answer properly anymore. Here is the strace output: accept(3, {sa_family=AF_INET, sin_port=htons(50611), sin_addr=inet_addr("127.0.0.1")}, [16]) = 5 fcntl64(5, F_GETFD) = 0 fcntl64(5, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 epoll_ctl(4, EPOLL_CTL_ADD, 5, {EPOLLIN|EPOLLERR|EPOLLHUP|EPOLLET, {u32=158310248, u64=158310248}}) = 0 epoll_wait(4, {{EPOLLIN, {u32=158310248, u64=158310248}}}, 128, -1) = 1 read(5, "GET /user/register HTTP/1.1\r\nHos"..., 4096) = 161 write(5, "HTTP/1.1 200 OK\r\nContent-Type: t"..., 106) = 106 <<<<< write(5, "00001000\r\n", 10) = -1 EPIPE (Broken pipe) <<<<< Why did the previous write() work fine but not this one? --- SIGPIPE (Broken pipe) @ 0 (0) --- As you can see, the client establishes a new connection which consequently is accepted. Then, it's added to the EPOLL queue. epoll_wait() signalises that the client sent data (EPOLLIN). The request is parsed and and a response is composed. Sending the headers works fine but when it comes to the body, write() results in an EPIPE. It is not a bug in "siege" because it blocks any incoming connections, no matter from which client.

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• Node.js fetching Twitter Streaming API - EADDRNOTAVAIL

  - by Jordan Scales

  I have the following code written in node.js to access to the Twitter Streaming API. If I curl the URL below, it works. However, I cannot get it to work with my code. var https = require('https'); https.request('https://USERNAME:[email protected]/1.1/statuses/sample.json', function(res) { res.on('data', function(chunk) { var d = JSON.parse(chunk); console.log(d); }); }); But I receive the following node.js:201 throw e; // process.nextTick error, or 'error' event on first tick ^ Error: connect EADDRNOTAVAIL at errnoException (net.js:642:11) at connect (net.js:525:18) at Socket.connect (net.js:589:5) at Object.<anonymous> (net.js:77:12) at new ClientRequest (http.js:1073:25) at Object.request (https.js:80:10) at Object.<anonymous> (/Users/jordan/Projects/twitter-stream/app.js:3:7) at Module._compile (module.js:441:26) at Object..js (module.js:459:10) at Module.load (module.js:348:31) If anyone can offer an alternative solution, or explain to me why this doesn't work, I would be very grateful.

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• what webserver / mod / technique should I use to serve everything from memory?

  - by reinier

  I've lots of lookuptables from which I'll generate my webresponse. I think IIS with Asp.net enables me to keep static lookuptables in memory which I can use to serve up my responses very fast. Are there however also non .net solutions which can do the same? I've looked at fastcgi, but I think this starts X processes, of which anyone can handle Y requests. But the processes are by definition shielded from eachother. I could configure fastcgi to use just 1 process, but does this have scalability implications? anything using PHP or any other interpreted language won't fly because it is also cgi or fastcgi bound right? I understand memcache could be an option, though this would require another (local) socket connection which I'd rather avoid since everything in memory would be much faster. The solution can work under WIndows or Unix... it doesn't matter too much. The only thing which matters is that there will be a lot of requests (100/sec now and growing to 500/sec in a year), and I want to reduce the amount of webservers needed to process it. The current solution is done using PHP and memcache (and the occasional hit to the SQL server backend). Although it is fast (for php anyway), Apache has real problems when the 50/sec is passed. I've put a bounty on this question since I've not seen enough responses to make a wise choice. At the moment I'm considering either Asp.net or fastcgi with C(++).

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• Is it possible to make a persistent connection between a Python web service and a .Net WCF Client?

  - by Ad Hock

  I have a .Net 3.5 SOAP client written in C# using the WCF. It's expecting basicHTTPBinding and a persistent connection with HTTP/1.1. I'm trying to create a Python 2.6 application that will act as a web-service for the client. My problem is that the client keeps closing the connection and opening a new one for every command to the web service. How does the .Net WCF client know to stay open when connecting with a .Net Service? When I create a dummy .Net web service the client connects fine and the connection remains persistent. From what I can tell, when connected to a .Net server, there are no special HTTP headers being sent, that makes sense since HTTP/1.1 assumes a persistent connection unless otherwise specified (right?). However, with the python web service I accept/open a connection and eventually the client will send a TCP FIN and the connection will close (the client never sends a FIN or RST when connecting to a .Net service). The communication goes something like this: Incoming -- HTTP Header for SOAP Command #1 Outgoing -- HTTP Header with a Continue Incoming -- Body of Command #1 Outgoing -- ACK Command #1 (HTTP headers and body) Incoming -- HTTP Header for SOAP Command #2 Outgoing -- HTTP Header with a Continue Incoming -- TCP FIN <Connection closes> <New connection opens and SOAP command #2 (with full HTTP headers) is sent> I'm using a SocketServer.ThreadingTCPServer as the server and a BaseHTTPServer.BaseHTTPRequestHandler for any requests. The handler is actually a derived class of that with a do_POST method to handle the HTTP headers. I've looked at WireShark captures and I'm stumped. I've tried setting socket options to SO_KEEPALIVE and SO_REUSEADDR in the server but that didn't seem to change anything. What am I missing?

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• How do I find out what process Id and thread id / name has a file open

  - by peter

  Hi All, I am using C# in an application and am having some problems with a file becoming locked. The piece of code does this, while (true) { Read a packet from a socket (with data in it to add to the file) Open a file Writes data to it Close a file } But in the process the file becomes locked. I don't really understand how, we are are definately catching and reporting exceptions so I don't see how the file doesn't get closed every time. My best guess is that something else is opening the file, but I want to prove it. Can someone please provide a piece of code to check whether the file is open and if so report what processid and threadid has the file open. For example if I had this code, StreamWriter streamWriter1 = new StreamWriter(@"c:\logs\test.txt"); streamWriter1.WriteLine("Test"); // code to check for locks?? StreamWriter streamWriter2 = new StreamWriter(@"c:\logs\test.txt"); streamWriter1.Close(); streamWriter2.Close(); That will throw an exception because the file is locked when we try and open it the second time. So where the comment is what could I put in there to report that the current app (process Id) and the current thread (thread Id) have the file locked? Thanks.

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• Android Multiple Handlers Design Question

  - by Soumya Simanta

  This question is related to an existing question I asked. I though I'll ask a new question instead of replying back to the other question. Cannot "comment" on my previous question because of a word limit. Marc wrote - I've more than one Handlers in an Activity." Why? If you do not want a complicated handleMessage() method, then use post() (on Handler or View) to break the logic up into individual Runnables. Multiple Handlers makes me nervous. I'm new to Android. Is having multiple handlers in a single activity a bad design ? I'm new to Android. My question is - is having multiple handlers in a single activity a bad design ? Here is the sketch of my current implementation. I've a mapActivity that creates a data thread (a UDP socket that listens for data). My first handler is responsible for sending data from the data thread to the activity. On the map I've a bunch of "dynamic" markers that are refreshed frequently. Some of these markers are video markers i.e., if the user clicks a video marker, I add a ViewView that extends a android.opengl.GLSurfaceView to my map activity and display video on this new vide. I use my second handler to send information about the marker that the user tapped on ItemizedOverlay onTap(int index) method. The user can close the video view by tapping on the video view. I use my third handler for this. I would appreciate if people can tell me what's wrong with this approach and suggest better ways to implement this. Thanks.

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• XSP2 crashes serving static images

  - by Dawkins

  Hi, Requesting a simple HTML page with a jpg image makes XSP2 crash. If I remove the image from the HTML then the page is served OK all the time. The version is XSP2 2.0 mono 2.6.1. the version 2.4.2.2 in the same machine works fine. I have tested it in two different machines, both Windows Vista Business SP1. Anyone has experienced the same? Any clue of what can be the problem? Below is the stack trace displayed by the console: (The line in Spanish says "it has been forced the interruption of an existing connection by the remote host") EDIT: since another user is having the same problem I have submited a bug to Novell and created a litle zip to reproduce the problem: https://bugzilla.novell.com/show_bug.cgi?id=582162 Peer unexpectedly closed the connection on write. Closing our end. System.IO.IOException: Write failure ---> System.Net.Sockets.SocketException: Se ha forzado la interrupción de una conexión existente por el host remoto. at System.Net.Sockets.Socket.Send (System.Byte[] buf, Int32 offset, Int32 size , SocketFlags flags) [0x00000] in <filename unknown>:0 at System.Net.Sockets.NetworkStream.Write (System.Byte[] buffer, Int32 offset, Int32 size) [0x00000] in <filename unknown>:0 --- End of inner exception stack trace --- at System.Net.Sockets.NetworkStream.Write (System.Byte[] buffer, Int32 offset, Int32 size) [0x00000] in <filename unknown>:0 at Mono.WebServer.XSPWorker.Write (System.Byte[] buffer, Int32 position, Int32 size) [0x00000] in <filename unknown>:0 Peer unexpectedly closed the connection on write. Closing our end. System.ObjectDisposedException: The object was used after being disposed. at System.Net.Sockets.NetworkStream.CheckDisposed () [0x00000] in <filename un known>:0 at System.Net.Sockets.NetworkStream.Write (System.Byte[] buffer, Int32 offset, Int32 size) [0x00000] in <filename unknown>:0 at Mono.WebServer.XSPWorker.Write (System.Byte[] buffer, Int32 position, Int32 size) [0x00000] in <filename unknown>:0 Thank you.

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• lightweight webserver to integrate on client end.

  - by Gopal

  Hi ,... I need to create a python module that will be installed on end-user machines. One of the scripts in that module should be able to receive http POSTS (usually with some JSON formatted data in the body) and then pass on that data to an appropriate python script. I can think of two ways to do this: a) Open a listening server socket on port 80, wait for that http request to come in, parse it and then pass that data to another python script depending on the url that arrived. This method will not require the end-user to install a webserver. End user only has to install the python module. b) Have a mini-webserver installed along with the python module. The webserver will do the same job as [a] via CGI without me requiring to write the CGI functionality. But then the user will have to install the web-server (ie., the hassle of yet another install). Would like to avoid that if possible. IF [b] is the easier option, what is the smallest simplest webserver there is (preferably one that can be packaged as part of the python module itself so that it does not have to be separately installed). Must be opensource of course. regards Gopal

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• How to File Transfer client to Server?

  - by Phsika

  i try to recieve a file from server but give me error on server.Start() ERROR : In a manner not permitted by the access permissions to access a socket was attempted to How can i solve it? private void btn_Recieve_Click(object sender, EventArgs e) { TcpListener server = null; // Set the TcpListener on port 13000. Int32 port = 13000; IPAddress localAddr = IPAddress.Parse("192.168.1.201"); // TcpListener server = new TcpListener(port); server = new TcpListener(localAddr, port); // Start listening for client requests. server.Start(); // Buffer for reading data Byte[] bytes = new Byte[277577]; String data; data = null; // Perform a blocking call to accept requests. // You could also user server.AcceptSocket() here. TcpClient client = server.AcceptTcpClient(); NetworkStream stream = client.GetStream(); int i; i = stream.Read(bytes, 0, 277577); BinaryWriter writer = new BinaryWriter(File.Open("GoodLuckToMe.jpg", FileMode.Create)); writer.Write(bytes); writer.Close(); client.Close(); }

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• XMLStreamReader and a real stream

  - by Yuri Ushakov

  Update There is no ready XML parser in Java community which can do NIO and XML parsing. This is the closest I found, and it's incomplete: http://wiki.fasterxml.com/AaltoHome I have the following code: InputStream input = ...; XMLInputFactory xmlInputFactory = XMLInputFactory.newInstance(); XMLStreamReader streamReader = xmlInputFactory.createXMLStreamReader(input, "UTF-8"); Question is, why does the method #createXMLStreamReader() expects to have an entire XML document in the input stream? Why is it called a "stream reader", if it can't seem to process a portion of XML data? For example, if I feed: <root> <child> to it, it would tell me I'm missing the closing tags. Even before I begin iterating the stream reader itself. I suspect that I just don't know how to use a XMLStreamReader properly. I should be able to supply it with data by pieces, right? I need it because I'm processing a XML stream coming in from network socket, and don't want to load the whole source text into memory. Thank you for help, Yuri.

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• Advice on designing and building distributed application to track vehicles

  - by dario-g

  I'm working on application for tracking vehicles. There will be about 10k or more vehicles. Each will be sending ~250bytes in each minute. Data contains gps location and everything from CAN Bus (every data that we can read from vehicle computer and dashboard). Data are sent by GSM/GPRS (using UDP protocol). Estimated rows with this data per day is ~2000k. I see there 3 main blocks. 1. Multithreaded Socket Server (MSS) - I have it. MSS stores received data to the queue (using NServiceBus). 2. Rule Processor Server (RPS) - this is core of this system. This block is responsible for parsing received data, storing in the database, processing rules, sending messages to Notifier Server (this will be sending e-mails/sms texts). Rule example. As I said between received bytes there will be information about current speed. When speed will be above 120 then: show alert in web application for specified users, send e-mail, send sms text. (There can be more than one instance of RPS). 3. Web application - allows reporting and defining rules by users, monitoring alerts, etc. I'm looking for advice how to design communication between RPS and Web application. Some questions: - Should Web application and RPS have separated databases or one central database will be enough? I have one domain model in web application. If there will be one central database then can I use the same model (objects) on RPS? So, how to send changed rules to RPS? I try to decouple this blocks as much as possible. I'm planning to create different instance of application for each client (each client will have separated database). One client will be have 10k vehicles, others only 100 vehicles.

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• My Thread Programs Block

  - by user315378

  I wrote a program that worked as a server. Knowing that "accept" was blocking the program. I wanted to launch a thread with this statement to prevent precisely that the program crashes, but this still happens. Can anybody help? Post code Thanks -(IBAction)Connetti{ if(switchConnessione.on){ int port = [fieldPort.text intValue]; labelStatus.text = [[NSString alloc] initWithFormat:@"Il Server è attivo"]; server_len = sizeof(server); server.sin_family = AF_INET; server.sin_port = htons((u_short)port); server.sin_addr.s_addr = INADDR_ANY; sd = socket (AF_INET, SOCK_STREAM, 0); bind(sd, (struct sockaddr*)&server, sizeof(server)); listen(sd, 1); [NSThread detachNewThreadSelector:@selector(startThreadAccept) toTarget:self withObject:nil]; } else { labelStatus.text = [[NSString alloc] initWithFormat:@"Server non attivo"]; switchChat.on = FALSE; switchChat.enabled = FALSE; } } -(void)startThreadAccept{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init]; [self performSelectorOnMainThread:@selector(acceptConnection) withObject:nil waitUntilDone:NO]; [pool release]; } -(void)acceptConnection{ new_sd = accept(sd, (struct sockaddr*)&server, &server_len); labelStatus.text = [[NSString alloc] initWithFormat:@"Ho accettato una connessione:%d", new_sd]; switchChat.enabled = TRUE; }

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• Simplest possible rack app -> permission error

  - by 7stud

  Here's the program(1.rb) blah blah blah blah blah blah: require 'rack' my_rack = lambda { |env| [200, {}, ["Hello. The time is: #{Time.now}"]] } handler = Rack::Handler::WEBrick handler.run(my_rack, :PORT => 12_500) Here's the error (blah blah blah blah blah): ~/ruby_programs$ ruby 1.rb [2012-12-07 21:49:09] INFO WEBrick 1.3.1 [2012-12-07 21:49:09] INFO ruby 1.9.3 (2012-04-20) [x86_64-darwin10.8.0] [2012-12-07 21:49:09] WARN TCPServer Error: Permission denied - bind(2) [2012-12-07 21:49:09] WARN TCPServer Error: Permission denied - bind(2) /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/utils.rb:85:in `initialize': Permission denied - bind(2) (Errno::EACCES) from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/utils.rb:85:in `new' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/utils.rb:85:in `block in create_listeners' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/utils.rb:82:in `each' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/utils.rb:82:in `create_listeners' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:82:in `listen' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:70:in `initialize' from /Users/7stud/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:45:in `initialize' from /Users/7stud/.rvm/gems/ruby-1.9.3-p194@programming/gems/rack-1.4.1/lib/rack/handler/webrick.rb:10:in `new' from /Users/7stud/.rvm/gems/ruby-1.9.3-p194@programming/gems/rack-1.4.1/lib/rack/handler/webrick.rb:10:in `run' from 1.rb:5:in `<main>' ~/ruby_programs$ Here's line 85 of ../webrick/utils.rb: sock = TCPServer.new(ai[3], port) If I replace the code in 1.rb with this: require 'socket' server = TCPServer.new 12_000 # Server bind to port 2000 loop do client = server.accept # Wait for a client to connect client.puts "Hello !" client.puts "Time is #{Time.now}" client.close end I don't get any errors, and if I enter the address: http://localhost:12000/ in my browser, I get the expected output: Hello ! Time is 2012-12-07 18:58:15 -0700

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• BackgroundWorker might be causing my application to hang

  - by alexD

  I have a Form that uses a BackgroundWorker to execute a series of tests. I use the ProgressChanged event to send messages to the main thread, which then does all of the updates on the UI. I've combed through my code to make sure I'm not doing anything to the UI in the background worker. There are no while loops in my code and the BackgroundWorker has a finite execution time (measured in seconds or minutes). However, for some reason when I lock my computer, often times the application will be hung when I log back in. The thing is, the BackgroundWorker isn't even running when this happens. The reason I believe it is related to the BackgroundWorker though is because the form only hangs when the BackgroundWorker has been executed since the application was loaded (it only runs when given a certain user input). I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread..any modifications I make to them is done in the UI thread through the progressChanged event. I do use Thread.Sleep in my worker thread to execute tests at timed intervals (which involves sending messages over a TCP socket, which was not created in the worker thread). I am completely perplexed as to why my application might be hanging. I'm sure I'm doing something 'illegal' somewhere, I just don't know what.

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• How should I read from a buffered reader?

  - by Roman

  I have the following example of reading from a buffered reader: while ((inputLine = input.readLine()) != null) { System.out.println("I got a message from a client: " + inputLine); } The code in the loop println will be executed whenever something appears in the buffered reader (input in this case). In my case, if a client-application writes something to the socket, the code in the loop (in the server-application) will be executed. But I do not understand how it works. inputLine = input.readLine() waits until something appears in the buffered reader and when something appears there it returns true and the code in the loop is executed. But when null can be returned. There is another question. The above code was taken from a method which throws Exception and I use this code in the run method of the Thread. And when I try to put throws Exception before the run the compiler complains: overridden method does not throw exception. Without the throws exception I have another complain from the compiler: unreported exception. So, what can I do?

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• how to do these in visio 2007?

  - by user285825

  I am very annoyed with this software. I am unable to do many things with this software. In the book 'UML distilled' many features of UML are discussed which I am not sure how to accomplish with visio 2007. For instance, 1) I can't find the unary association. In the UML static structure under shapes panel on left, there are a lot of components like package, class, blah, blah, binary association, blah, blah, association class. But where is unary association. 2) For sequence diagram, I created a message (any of sync, async, call type message, ordinary message). The I tried to incorporate some parameter information. I went to the properties. There were a category called arguments. But selecting that shows a table where arguments are supposed to be shown. But all are diasbled. 3) For sequence diagram, there is no component delete (the big X) in the UML Sequence. 4) For class diagram, there is supposed to be a comment compartment where comments like mentioning the responsibilities are allowed using a comment prefixed with "--". But I am not sure how to accomplish them. 5) there is also supposed to be a way to indicate static properties of a class. But I am not sure how to do that in visio. 6) there is supposed to be a stereotype for class <. But in the stereotype drop down there is no stereotype. 7) where is the ball and socket component?

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